The File Output node does now allow empty names for its sockets, so
doing things like flat RGBA pass in an unnamed layer is impossible,
which was possible before the recent redesign of the node. To allow
this, socket items accessors now have an option to allow empty names.
Implementation wise, the non-default variant of BLI_uniquename_cb was
used to make the empty name replacement optional. Incidentally, the new
function is more CPP friendly, so the MAX_NAME length limitation was
lifted.
Pull Request: https://projects.blender.org/blender/blender/pulls/144334
c7b77b2b9f